Description of problem:
The completed Pulp tasks stay forever and never be purged by Pulp. For a busy Satellite environment, the number of completed tasks can easily reach millions of records.

Large tasks table may cause the following issues:

1. Large core_task table size (more than 10GB)
2. Affecting Pulp performance related to pulp task queries.

For example. we can see the following slow queries of core_task table in the database logs.
~~~
duration: 5173.306 ms statement: SELECT 1 AS "a" FROM "core_task" WHERE ("core_task"."pulp_created" < 'xxxxxxxxxxxxx'::timestamptz AND "core_task"."state" IN ('waiting', 'running', 'canceling') AND "core_task"."reserved_resources_record" && (ARRAY['/pulp/api/v3/domains/xxxxxxxxxxxxxxxxxxxxxxxxxxxx/', '/api/v3/distributions/', 'shared:/api/v3/distributions/'])::text[]) LIMIT 1

duration: 6680.679 ms statement: SELECT 1 AS "a" FROM "core_task" WHERE ("core_task"."pulp_created" < 'xxxxxxxxxxxxx'::timestamptz AND "core_task"."state" IN ('waiting', 'running', 'canceling') AND "core_task"."reserved_resources_record" && (ARRAY['/pulp/api/v3/domains/xxxxxxxxxxxxxxxxxxxxxxxxxxxx/', '/api/v3/distributions/', 'shared:/api/v3/distributions/'])::text[]) LIMIT 1
~~~

Additional info:
The workaround to use pulp command to purge the tasks.

E.g. the below command will purge the completed tasks older than 2 weeks.
~~~
pulp -force task purge --finished-before $(date --date="$(date) -2 week" +%Y%m-%d) --state completed --state failed --state canceled
~~~

QE Tracker for https://issues.redhat.com/browse/SAT-25155
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2280509